Karoshi is a Japanese term that translates directly to “death by overwork.” It refers to fatal heart attacks, strokes, and other cardiovascular events caused by chronic excessive work hours and occupational stress. First recognized in Japan in the 1980s, karoshi became a formal category of workplace injury eligible for government compensation, and the concept has since drawn global attention as overwork-related health problems spread well beyond Japan’s borders.
How Overwork Leads to Death
Karoshi typically kills through cardiovascular events: heart attacks, strokes, heart failure, and ruptured blood vessels. The path from long hours to a fatal event isn’t a single clear-cut mechanism but a buildup of overlapping damage. Chronic work stress, especially in jobs with high demands and little personal control, triggers a sustained physiological strain on the cardiovascular system. Over time, this contributes to a cluster of risk factors including higher blood pressure, elevated blood sugar, excess abdominal fat, and unhealthy cholesterol levels.
A landmark study of British civil servants found that the more frequently workers reported this kind of high-demand, low-control stress over repeated assessments, the greater their risk of developing this dangerous cluster of metabolic problems. That metabolic damage explained roughly 15% of the link between chronic job strain and coronary heart disease. The remaining risk comes from other stress pathways, including inflammation, hormonal disruption, and the behavioral changes stress provokes. Workers under sustained job strain are more likely to become physically inactive, smoke more heavily, and drink more alcohol, all of which compound cardiovascular risk.
Sleep deprivation plays a central role. Workers logging extreme overtime simply don’t have enough hours left for adequate rest, and chronic sleep loss independently raises blood pressure, disrupts metabolism, and increases the likelihood of a sudden cardiac event.
The 80-Hour Overtime Threshold
Japan’s Ministry of Health, Labour, and Welfare draws a specific line: 80 hours of overtime per month is the point at which overwork becomes strongly correlated with karoshi. This figure, known informally as the “karoshi line,” serves as the primary benchmark for workers’ compensation claims. Cases in which an employee dies from a stroke or heart attack after sustained overtime near or above this threshold can be officially recognized as industrial accidents, making the worker’s family eligible for compensation.
Japan’s general labor rules cap overtime at 45 hours per month and 360 hours per year, but companies can exceed these limits if their labor unions agree. In practice, the cap is regularly exceeded. A Tokyo newspaper investigation found that 70% of the top 100 companies listed on the Tokyo Stock Exchange allowed employees to work beyond the 80-hour karoshi threshold.
Karojisatsu: Suicide From Overwork
Karoshi has a companion term: karojisatsu, meaning “overwork suicide.” This refers to workers, often in their twenties and thirties, who develop severe mental illness under the weight of excessive work hours and take their own lives. Japanese law now treats these deaths not as voluntary acts but as the result of mental illness caused by workplace conditions. Workers who develop depression or other psychiatric disorders from overwork are eligible for compensation, and families of those who die by suicide can file claims.
Public awareness of karojisatsu surged in 2000, when Japan’s Supreme Court ordered a major corporation to compensate the family of a man who had killed himself after prolonged extreme overwork. That ruling helped establish the legal framework that exists today. In fiscal year 2024, Japan recognized 1,055 compensation cases for work-related mental disorders, including 88 suicides.
Who Is Most at Risk
The two forms of karoshi strike different age groups. Cardiovascular deaths from overwork occur most often in middle-aged workers, with an average onset age of about 49 for both men and women. Mental health disorders linked to overwork, including those leading to suicide, hit younger. Among men, the average age was 40. Among women, it was closer to 37. Over half of male compensation cases for work-related mental disorders involved workers in their twenties or thirties, and for women the figure was 61%.
Certain industries carry disproportionate risk. For cardiovascular deaths among men, nearly a third of compensated cases came from transport and postal services, followed by wholesale and retail trade, then manufacturing. For mental health disorders, manufacturing led among men, while medical, health, and welfare work accounted for nearly 29% of compensated cases among women. The common thread across these sectors is a combination of long hours, high psychological demands, and limited autonomy.
Scale of the Problem
In fiscal year 2024, Japan officially compensated 241 cases of work-related cardiovascular disease, 67 of which were fatal. These numbers reflect only the cases that cleared the high bar for formal recognition. The actual toll is almost certainly larger, since many families never file claims, and borderline cases may not meet the strict overtime documentation requirements.
The problem extends far beyond Japan. A joint analysis by the World Health Organization and the International Labour Organization estimated that in 2016, roughly 488 million working-age people globally were exposed to long working hours (defined as more than 55 hours per week). Of an estimated 1.9 million work-related deaths worldwide, long working hours accounted for approximately 800,000, making it the single largest occupational risk factor, responsible for 40% of all work-related deaths. Most of these deaths were from heart disease and stroke, the same causes that define karoshi.
Prevention Efforts
Japan has pursued several policy interventions. One prominent measure is the concept of a minimum daily rest period between shifts, designed to ensure workers get enough sleep to recover from occupational fatigue. The government has also pushed “work style reform” legislation aimed at capping overtime and changing corporate culture around long hours.
Experts caution that reducing hours alone won’t solve the problem. If companies cut overtime without reducing workloads, the result is simply higher-intensity work crammed into fewer hours, which carries its own health risks. Effective prevention requires changing the actual volume of tasks, improving how work is organized, and shifting the deep cultural expectation that long presence at the office signals dedication. In industries like healthcare and transportation, where services can’t simply be reduced, the solution often means hiring more workers to distribute the load.